<form method="get" id="searchform" action="<?php echo home_url(); ?>">
    <input type="text" id="search_input" value="Search..." name="s" onfocus="if(this.value=='Search...') this.value='';" onblur="if(this.value=='') this.value='Search...';" />
    <input type="submit" id="searchsubmit" value="" />
</form>
